Accessory drive system for an automotive engine

Abstract

An accessory drive system for an automotive engine includes a drive pulley attached to an output shaft of the engine and a flexible drivebelt for connecting the drive pulley with driven pulleys. A tensioner maintains the drivebelt in contact with each of the drive and driven pulleys. The tensioner includes an arm which is rotatably mounted to the engine which has a wheel for contacting the drivebelt. The wheel is urged into contact with the drivebelt by the arm, with the tensioner further including a governor for controlling rotational motion of the arm with the arm being able to rotate freely in the direction in which tension of the drivebelt is increased, with the governor resisting motion of the arm in the direction in which tension in the drivebelt is decreased.

We claim: 
     
       1. An accessory drive system for an automotive engine, comprising: a drive pulley attached to an output shaft of the engine;   a flexible drive belt for connecting the drive pulley with a plurality of driven pulleys, with one driven pulley located upon each of a plurality of driven devices; and   a tensioner for maintaining the drive belt in contact with each of said drive and driven pulleys, with said tensioner comprising an arm which is rotatably mounted to the engine and which has a wheel for contacting the drive belt, with the wheel being urged into contact with the drive belt by the arm, and with said tensioner further comprising a governor for controlling the rotational motion of the arm such that the arm will be freely able to rotate in the direction in which the tension in the drive belt is increased, with said governor resisting motion of the arm in the direction in which tension in the drive belt is decreased, wherein said governor comprises a hydraulic strut interposed between said tensioner arm and a mounting surface fixed to the engine adjacent the tensioner, such that linear motion of the strut accompanies rotational motion of the arm, with the strut having a connecting rod portion being able to move freely in the direction in which tension in the drive belt is increased, while resisting movement in the direction in which tension in the drive belt is decreased.   
     
     
       2. An accessory drive system according to claim 1, wherein the hydraulic strut comprises a piston reciprocably mounted within a cylinder upon said connecting rod, with the connecting rod having a free end attached to the tensioner arm such that the piston slides within the cylinder as the tensioner arm rotates, with the motion of the piston being controlled by hydraulic fluid contained within the cylinder such that motion of the piston in the direction which allows the tensioner to rotate in the direction in which the tension in the drive belt is increased is substantially uninhibited, but motion of the piston in the direction in which the tensioner allows the tension within the drive belt to decrease is restrained by hydrostatic force within the cylinder. 
     
     
       3. An accessory drive system according to claim 2, wherein hydrostatic force is maintained within the cylinder by causing fluid leaving the cylinder under a compressive force generated by the piston to flow through a restrictive orifice when the piston is moving in the direction in which tension within the drive belt is decreased, with the strut having a parallel flow channel which is valved so as to allow fluid to flow freely from the cylinder when the piston is moving in the direction in which tension within the drive belt is increased. 
     
     
       4. An accessory drive system according to claim 1, wherein the hydraulic strut comprises a piston reciprocably mounted within a cylinder upon said connecting rod, with the connecting rod having a free end attached to the tensioner arm such that the piston slides within the cylinder as the tensioner arm rotates, with the motion of the piston being controlled by hydraulic fluid supplied to the cylinder such that motion of the piston in the direction so as to allow the tensioner to rotate in the direction in which the tension in the drive belt is increased is substantially uninhibited, but motion of the piston in the direction in which the tensioner allows the tension within the drive belt to decrease is selectively restrained by hydrostatic force within the cylinder. 
     
     
       5. An accessory drive system according to claim 4, wherein hydrostatic force is selectively maintained within the cylinder by causing fluid leaving the cylinder under the compressive force of the piston to flow through either a restrictive orifice or a bypass channel when the piston is moving in the direction in which the tension within the drive belt is decreased, with flow through the bypass channel being controlled by a solenoid valve operated by an electronic controller such that when the solenoid valve is open, motion of the piston will be unrestrained in both directions. 
     
     
       6. An accessory drive system according to claim 5, wherein said electronic controller operates said solenoid valve such that rotational motion of the arm is restricted during periods of operation characterized by rapid engine deceleration. 
     
     
       7. An accessory drive system according to claim 5, wherein said electronic controller operates said solenoid valve such that rotational motion of the arm is restricted when engine speed exceeds a predetermined value. 
     
     
       8. An accessory drive system according to claim 1, wherein said governor comprises an electronically lockable strut interposed between said tensioner arm and a mounting point adjacent the tensioner, such that linear motion of the strut accompanies rotational motion of the arm unless the strut is locked. 
     
     
       9. An accessory drive system according to claim 8, wherein said strut comprises a slidable, geared rack which is lockable in a plurality of linear positions by a solenoid actuated plunger engageable with the gear teeth of said rack, with said plunger being operated by an electronic controller. 
     
     
       10. An accessory drive system according to claim 9, wherein said electronic controller operates said plunger such that rotational motion of the arm is restricted during periods of operation characterized by rapid engine deceleration. 
     
     
       11. An accessory drive system according to claim 9, wherein said electronic controller operates said plunger such that rotational motion of the arm is restricted when engine speed exceeds a predetermined value. 
     
     
       12. An accessory drive system according to claim 1, wherein said governor comprises an electronically piloted sliding friction wedge plunger located within a strut interposed between said tensioner arm and a mounting point adjacent the tensioner, such that linear motion of the strut accompanies rotational motion of the arm unless the strut is locked. 
     
     
       13. An accessory drive system for an automotive engine, comprising: a drive pulley attached to an output shaft of the engine;   a flexible drive belt for connecting the drive pulley with a plurality of driven pulleys, with one driven pulley located upon each of a plurality of driven devices;   a tensioner for maintaining the drive belt in contact with each of said drive and driven pulleys, with said tensioner comprising an arm which is rotatably mounted to the engine and which has a wheel for contacting the drive belt, with the wheel being urged into contact with the drive belt by the arm, and with said tensioner further comprising a governor for controlling the rotational motion of the arm such that the arm will be freely able to rotate in the direction in which the tension in the drive belt is increased, with said governor selectively resisting motion of the arm in the direction in which tension in the drive belt is decreased; and   an electronic controller for operating the governor in response to at least one sensed engine parameter, such that movement of the arm in the direction in which tension in the drive belt is decreased will effectively be prevented in the event that the value of the sensed parameter indicates that the engine is operating in a mode in which the tension would otherwise be decreased.   
     
     
       14. An accessory drive system according to claim 12, wherein said electronic controller operates said governor such that rotational motion of the arm is restricted during periods of operation characterized by rapid engine deceleration. 
     
     
       15. An accessory drive system according to claim 12, wherein said electronic controller operates said governor such that rotational motion of the arm is restricted when engine speed exceeds a predetermined value. 
     
     
       16. A method for controlling the tension of a flexible drive belt in an accessory drive system for an automotive engine, comprising the steps of: sensing at least one engine operating parameter indicative of engine operation in a mode tending to decrease tension in the drivebelt below a threshold at which traction of the belt is adequate to avoid slipping of the belt; and   upon sensing a value of said at least one operating parameter corresponding to a value of drive belt tension below said threshold, directing a tensioner associated with said accessory drive system to change from a mode in which the tensioner compliantly tensions the drive belt to a mode in which the tensioner noncompliantly tensions the drive belt so as to prevent the tension from decreasing.